<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* 实现盒子水平居中 */
        * {
            margin: 0;
            padding: 0;
        }
        .box {
            /* 假设盒子宽100高100 */
            width: 100px;
            height: 100px;
            background-color: orange;
            /* 水平居中方法一 */
            margin: 0 auto;
        }
    </style>
</head>

<body>
    <div class="box"></div>
</body>

</html>